Network Working Group                                 W. Simpson, Editor
Request for Comments: 1661                                    Daydreamer
STD: 51                                                        July 1994
Obsoletes: 1548
Category: Standards Track


                   The Point-to-Point Protocol (PPP)



Status of this Memo(略)

Abstract(略)


1.  Introduction

   The Point-to-Point Protocol is designed for simple links which
   transport packets between two peers.  These links provide full-duplex
   simultaneous bi-directional operation, and are assumed to deliver
   packets in order.  It is intended that PPP provide a common solution
   for easy connection of a wide variety of hosts, bridges and routers
   [1].

   Encapsulation

      The PPP encapsulation provides for multiplexing of different
      network-layer protocols simultaneously over the same link.  The
      PPP encapsulation has been carefully designed to retain
      compatibility with most commonly used supporting hardware.

      Only 8 additional octets are necessary to form the encapsulation
      when used within the default HDLC-like framing.  In environments
      where bandwidth is at a premium, the encapsulation and framing may
      be shortened to 2 or 4 octets.

      To support high speed implementations, the default encapsulation
      uses only simple fields, only one of which needs to be examined
      for demultiplexing.  The default header and information fields
      fall on 32-bit boundaries, and the trailer may be padded to an
      arbitrary boundary.

   Link Control Protocol

      In order to be sufficiently versatile to be portable to a wide
      variety of environments, PPP provides a Link Control Protocol
      (LCP).  The LCP is used to automatically agree upon the
      encapsulation format options, handle varying limits on sizes of
      packets, detect a looped-back link and other common
      misconfiguration errors, and terminate the link.  Other optional
      facilities provided are authentication of the identity of its peer
      on the link, and determination when a link is functioning properly
      and when it is failing.

   Network Control Protocols

      Point-to-Point links tend to exacerbate many problems with the
      current family of network protocols.  For instance, assignment and
      management of IP addresses, which is a problem even in LAN
      environments, is especially difficult over circuit-switched
      point-to-point links (such as dial-up modem servers).  These
      problems are handled by a family of Network Control Protocols
      (NCPs), which each manage the specific needs required by their
      respective network-layer protocols.  These NCPs are defined in
      companion documents.

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